Generally, there is a large amount of heat generated in a data center since many servers are placed in the data center. Normal operation of the servers requires that air conditioning be properly controlled to keep environmental conditions for a server room in a predetermined range.
Technology for cooling air in a room in which many computers are installed as in the data center has been known from JP, P2005-172309A. JP, P2005-172309A discloses an air conditioning system configured such that air sucked in from a space in the lower portion of the room is blown out from a space in the upper portion of the room and thereby the air is sucked into upper portions of server racks.
This technology enables efficient air conditioning control by reducing temperature gradients throughout the entire area in the room and also reducing variations in supply air temperature.
The data center in which load on an object to be air conditioned is information equipment has different features from those of typical buildings. For example, the features are that:                most of the load is sensible heat load;        the set temperature and humidity fall within a certain range; and        ventilation for preventing an increase in CO2 concentration is unnecessary since the load does not generate CO2.        
However, the conventional data center wastes energy because of not performing air conditioning control adapted for these features.
An object of the present invention is to provide an air conditioning system and an air conditioning control method for a server room, capable of performing air conditioning control having a great energy-saving effect with efficiency and reliability.